The Codex Regius of the Poetic Edda (GKS 2365 4to) is one of the most important medieval Icelandic manuscripts. It contains many eddic poems, most of them only preserved in it, interspersed with prose passages providing the narrative background and context. The section of the manuscript about the youth of the hero Sigurðr (folios 26v–32v) is one of the least studied parts of the manuscript. Traditionally divided by editors into one prose passage (Frá dauða Sinfjǫtla) and four poems (Grípisspá, Reginsmál, Fáfnismál and Sigrdrífumál), it offers unique opportunities that have so far been missed to reassess the manuscript’s form and content through a combination of palaeography, philology, and literary analysis. The dissertation opens with an introduction outlining the main critical issues in the interpretation of the section, the most significant trends in past scholarship on it, and the principles upon which my approach is based. Some long-standing assumptions and the problems they entail are presented, highlighting the necessity to question and update them. The bulk of the dissertation is divided into two parts. Using the tools of palaeography and philology, Part 1, entitled ‘Compositional History’, offers an analysis of how the section was created. It starts with an examination of the paratext associated with the section in modern editions and in the manuscript, showing considerable and problematic differences between the two. Palaeographical analysis is then used to establish correlations between different types and combinations of large initials and headings on the one hand, and the types of divisions between compositions that they signal on the other. A new, manuscript-based subdivision of the materials in the young Sigurðr section is subsequently presented. The rest of Part 1 focuses on the Reginsmál-Fáfnismál-Sigrdrífumál complex. After a survey of the formal features that set it apart from the rest of the section and, indeed, the rest of the manuscript, the prosimetrum is compared to that of Helgakviða Hjǫrvarðssonar and Helgakviða Hundingsbana II, the only formally analogous section in the Codex Regius. A series of clues from both prosimetric sequences is examined in detail to establish how and by whom these compositions were created, updating old views and reaching new conclusions. In the light of this analysis, the similarities between the two sequences are revisited to suggest possible reasons behind their peculiar form. Part 1 ends with an overview of the layers of composition identifiable in the young Sigurðr section as a whole, including its prose introduction and Grípisspá. Part 2, ‘Interpretative Reading’, offers a reading, interpretation, and literary analysis of the whole young Sigurðr section. Each of the episodes of which it is composed is analysed and interpreted taking into account its compositional history and its relationship with the rest of the section. Close reading of some significant passages is combined with the analysis of narrative structure and mode, plot and characters, themes and their development, echoes and variations, and other literary elements across the whole section. Comparison with other primary sources is used to illuminate the role of the compiler and his handling of source materials. Through philological analysis, new answers to old questions, such as whether Sigrdrífa and Brynhildr are the same character, are found. The section is revealed as a unified whole focusing on the instruction of the hero and serving as a frame to showcase wisdom passages and reflections on key heroic concepts emerging from poetic dialogue. A conclusion to the dissertation brings together and expands the results of the analysis in both Part 1 and 2, drawing out their implications in full and reconsidering what the young Sigurðr section is, how it was created, and how it should be read. Some principles on which new editions of it should be based in order not to misrepresent it are then proposed. Conclusions are drawn about the ways in which the results of my analysis impact our consideration of the Codex Regius as a whole and its unique place in Old Norse literature alongside other products of the processes of recording of oral tradition. To close, avenues for further research are outlined.